Muirchertach Ua Briain (1050-1119) was the son of Tairrdelbach (d. 1086), son of Tadc (d. 1023), son of Brian Boru, the latter’s most successful successor as king of Dal Cais, Munster, and Ireland. The Annals of Tigernach (perhaps anachronistically) record his birth in 1050, and he otherwise appears on record only in 1075 when his father led the armies of Munster, Leinster, Osraige, Mide, Connacht, and Dublin to Ardee, County Louth, to gain submission from the Airgialla and Ulaid; the former stood their ground at Ard Monann (unidentified) where they slaughtered the Munstermen under Muirchertach, described as rigdamna Muman, "makings of a king of Munster" (AFM). In the same year, his father appointed him king of Dublin with which he was sporadically associated for the rest of his life. He then disappears without a trace until October 29, 1084 when he and the forces of Dublin, Leinster, Osraige, and Munster defeated Donnchad Ua Ruairc of Uf Briuin Breifne at Moin Cruinnioce, near Leixlip, County Kildare (a Norse settlement which he may have ruled from Dublin). In this major battle 4,000 were killed, Muirchertach cutting off Ua Ruairc’s head and bringing it back to his father’s palace at Limerick.
When Tairrdelbach died in 1086, Munster was divided between his three sons, Tadc, Diarmait, and Muirchertach. Tadc died within a month, and Muirchertach banished Diarmait and seized the whole province. In 1087, he fought a battle against Diarmait and the king of Leinster at Raith Etair (possibly the promontory fort at the tip of Howth Head), and Muirchertach’s forces triumphed. In 1088, he sent one fleet up the Shannon as far as Incherky, south of Clonfert, where the king of Connacht, Ruaidrf na Saide Buide Ua Conchobair, father of the great Tairrdelbach, slaughtered Muirchertach’s men. Another Munster fleet sent around the west coast was also slaughtered, the Connacht army then invading Corco Mruad (the Burren, Co. Clare).
Domnall Mac Lochlainn, king of the Northern Uf Neill, now emerged as Ua Briain’s rival for supremacy, allying with the sons of Muirchertach’s uncle Donnchad mac Briain (d. 1064) by marrying the daughter of his grandson Cennetig (d. 1084), who had been king of Telach Oc in Tfr nEogain with Mac Lochlainn’s support. In 1088, the latter attacked Connacht and forced its king to submit, and then together they marched on Munster in Ua Briain’s absence in Leinster; Limerick, Kincora, and Emly were burned and 160 hostages seized, whom Muirchertach later bought back with cattle, horses, gold, silver, and meat, victory being symbolically sealed when the severed head of Donnchad Ua Ruairc was brought back to Connacht. A Munster source claims that Ua Briain avenged himself in 1089 by invading Mide and Leinster, whose king he killed, making himself king of Leinster and Dublin, before proceeding to Connacht to cut down the sacred inaugural tree of the Connachtmen. Other annals suggest Muirchertach did not gain the kingship of Leinster and Dublin and had no role in killing the Leinster king (apparently assassinated by kinsmen), a version of events borne out by the fact that his men burned Lusk in Fine Gall, killing 160 church occupants, suggesting that it (and presumably Dublin) was in enemy hands.
Also in 1089, Muirchertach sailed to Lough Ree and looted its islands, but Ua Conchobair blocked the Shannon near Clonmacnoise, denying the Munster ships a route home. Driven back to Athlone, they were forced to surrender both ships and supplies to the king of Mide, Domnall Ua Mael Sechnaill, returning home under safe conduct overland while the Connacht and Mide armies sailed the confiscated vessels southward, purportedly reducing the Plain of Cashel to a desert. In 1090 Ua Briain, Mac Lochlainn, Ua Conchobair, and Ua Mael Sechnaill held a conference that resulted in the three other kings giving hostages (presumably in submission) to Mac Lochlainn, before departing in peace. But Muirchertach was on the march again in Mide that same year, though he was defeated by Ua Mael Sechnaill who invaded Munster, as did Ua Conchobair at about the same time. Ua Briain then marched into Connacht, raided Leinster along with the men of Dublin (which he had obviously retaken), and marched to Athboy in Brega, where Mac Lochlainn apparently aided him against Ua Mael Sechnaill.
Ua Conchobair invaded Munster again in 1091 but was blinded in the following year, whereupon Muirchertach led an army into the province, took its hostages, and, according to the Inisfallen Annals, assumed the high kingship of Connacht. In 1092, Ua Briain expelled (temporarily) the ruling dynasty of Connacht into Tfr nEogain, and the king of Mide came to Limerick to submit to him, while in 1094 he unprec-edentedly partitioned Mide between two rival members of the Uf Mael Sechnaill. His contemporary power is evident from the request by the nobility of Man and the Isles to provide a ruler following their king’s death in 1095, whereupon Muirchertach apparently found an outlet for the wayward energies of his nephew, Domnall mac Taidc, by dispatching him to Man. Two ominous expeditions by the Norse king Magnus III ("Barelegs") in 1098 and 1102-1103, were skillfully handled by Ua Briain, who bought off Norse aggression in 1102 by marrying his daughter to Magnus’s younger son (though the threat dissipated following Magnus’s killing by the Ulaid in 1103). He likewise improved relations with the Normans of South Wales when, in 1101, another daughter was married off to Arnulf de Montgomery, then in rebellion against the new English king, Henry I: when the latter responded with a trade blockade, Muirchertach apparently relented, but Arnulf is said to have fled to Ireland hoping to succeed him as king, and Muirchertach later wrote to Anselm of Canterbury thanking him for interceding with Henry on his son-in-law’s behalf.
Now the dominant figure in Ireland, as king of Munster and usually overlord of Osraige, Leinster, Dublin, Mide, and Connacht, Muirchertach nevertheless discovered (like his father and his great-grandfather, Brian Boru) that his authority remained incomplete. Each year his vast interprovincial army went north to Assaroe on the Erne or the Sliab Fuaid/Mag Muirthemhne area on the southeastern frontier of Ulster, only to be forced back, often following the intervention of the comarbae Patraic (the abbot of Armagh) to secure a year’s truce. In 1100, for example, he led "the men of Ireland" to Assaroe to force Cenel Conaill to submit, simultaneously sending the Dublin fleet around the coast to Inishowen, but was forced to retreat, and the fleet was massacred. In 1101, he was appropriately called for the first time "king of Ireland" in the Annals of Tigernach, and made his most spectacular campaign yet, called An Slogadh Timcheall (the Circular Hosting) by the other annals. The six-week expedition again involved the armies of all the provinces, save those of the north, marching to the Erne at Assaroe, then on to Inishowen, burning en route Ardstraw and Fahan, and culminating in the demolition of Grianan of Ailech in revenge for Mac Lochlainn’s earlier destruction of Kincora. Muirchertach’s men were ordered to bring back to Limerick one stone for every sack of provisions they had, and his forces returned home along the ancient Slige Midluachra. For the first time, Ulaid was successfully invaded and its submission won, making Ua Briain master of all Ireland except for the northwestern corner which, though undermined, had not submitted and never did. Muirchertach regularly returned, sometimes with disastrous consequences, as in 1103 when (following his possibly conscious emulation of Brian Boru in making a donation of gold to Armagh) his allies were severely routed by Mac Lochlainn in the battle of Mag Coba; but usually the annual expedition ended in stalemate in what is now South Armagh.
In 1101, following his father’s example, he presided over the Synod of Cashel, which attempted to reduce lay interference in church affairs, saw Cashel being handed to the church in perpetuity, and prohibited marriage within specified degrees of consanguinity. It was probably at Muirchertach’s behest about this juncture that the propaganda tract known as Cogad Gaedel re Gallaib ("The war of the Irish with the foreigners") was composed. Combining annalistic data with romantic embellishments allegedly recounting the exploits of Brian Boru against his Norse and other enemies, in fact it uses Brian as a paradigm for Muirchertach and seeks to glorify his reign. The culmination of the latter was perhaps his institution of another reform synod at Raith Bressail in 1111, in which a formal territorial diocesan structure was established for the country, and two ecclesiastical provinces established at Armagh and Cashel, the former having primacy.
But political opposition remained. In 1112, Domnall Mac Lochlainn defied him by marching to Dubgaill’s Bridge in Dublin, raiding Fine Gall, and carrying off livestock and prisoners. In the same year, Domnall invaded Ulaid, annexing part of it, which he intended to rule in person. Muirchertach came to Ulaid in response, Mac Lochlainn moved his armies to Mag Coba ready for battle, and the comarbae Patraic intervened to secure a truce. But the Munster army remained encamped for a month in Brega, Mac Lochlainn’s forces observing from the lands of Fir Rois, County Louth, both prepared for war. Domnall’s strength is apparent from his refusal to negotiate, although the crisis was again resolved by intervention from Armagh.
Muirchertach’s position was weakened further by opposition from his brother Diarmait and the sons of Tadc. His own intended heir, his son Domnall, was proving a disappointment (his nickname ger-rlamhach ("short-armed") may indicate a disability). The convention of apprenticing the heir to Dublin had been followed, and Domnall managed one major success in battle there in 1115, but subsequently vanished from view and ended his days in monastic obscurity. Muirchertach fell dangerously ill in 1114 whereupon the kingship was seized by his brother Diarmait. When Muirchertach recovered in 1115 and set about regaining his kingdom, his principal ally was Brian (d. 1118) son of Murchad (d. 1068) son of Donnchad mac Briain, his own father’s archenemy. He needed all the support he could get, since Domnall Mac Lochlainn reacted to news of the high king’s illness by forcing the submissions of Ulaid, Mide, and Breifne. But, being of similar age to Muirchertach, his day had passed.
Tairrdelbach Ua Conchobair was the new aspirant to national power and had invaded Thomond in 1115. Ua Briain’s problems were eased by the death in that year of his troublesome nephew Domnall mac Taidc, and he took to the campaign trail again in Osraige, Leinster, and Brega, but pressure from Ua Conchobair’s repeated invasions of Munster finally forced Muirchertach’s resignation of the kingship of Munster to his brother Diarmait and his own retirement to Lismore. When Diarmait died in 1118, Ua Conchobair partitioned Munster, giving Desmond to Tadc Mac Carthaig and Thomond, not to Muirchertach’s sons, but to those of Diarmait. Muirchertach was dead within a year, the Inisfallen annalist tersely recording his passing in the words "Murchertach Ua Briain, r( Erend, fo buaid aithirgi quieuit [Muirchertach Ua Briain, king of Ireland, rested after a victory of repentance]," the Annals of Ulster calling him "the tower of the honour and dignity of the Western World." All future kings of Thomond were descended from his brother Diarmait, his son son Mathgamain being ancestors of the MacMahons of Corco Baiscind.
